Aerial vehicles are used today in various missions of delivery of fluids and granular substances from the air. In some cases, delivery from the air is the only option either due to limited access or because of the effectiveness of the air delivery in covering large areas in a short time. Non-limiting examples for such mission include firefighting, fertilizing, cooling nuclear reactors as well as using herbicides and pesticides.
The main challenge in delivering fluids and granular substances, due to their particle nature, is the tendency of these materials to be greatly affected by air resistance. Specifically, large portions of the fluids transform into an aerosol which drifts by the wind and never reaches the target on the ground or above it. The aerosol may also affect the aerial vehicle or people on board it or on the ground. In a case that the fluid contains harmful ingredients, the aerosol or other buoyant particles can cause health problems or harm the aerial vehicle. Solid granular substances suffer from similar limitations and, while they do not transform into aerosol, their air resistance is sufficiently high such that they may lose their ballistic characteristics.
In order to avoid the aforementioned aerosol effect, aerial flights today are performed at low altitudes (less than 100 feet above ground). Such a flight profile is very risky, and requires special aircrafts and special pilot skills. Because of those high requirements, current aerial missions can be performed nowadays only at day time and they are stopped altogether during the night, or in strong wind and low visibility conditions, such as smoke, fog or dust.
FIG. 1 is a schematic illustration of an aerial vehicle 10 discharging fluid 40 from the air towards targets 20 such as trees on the ground 30. Due to the aforementioned air resistance, some portions 50 of the fluid are cut from the main bulk of fluid 40 while other portions of fluid 40 transform into aerosol 60. As the aerosol loses its ballistic character it becomes very difficult, if not impossible, to deliver effective amounts of fluid 40 to ground 30 or targets 20. It is noted that the aforementioned problem becomes ever more challenging when air vehicle 10 is located higher up in the sky.
After hitting the ground, a material that will not be consumed by fire or be used as a fertilizer may contaminate the ground. Accordingly, any attempt to encapsulate the fluid inside specially designed packages (e.g., shells) must take into consideration the environmental effect to these packages. Accordingly, materials such as polymers that can be disintegrated and/or undergo biodegradation may be considered.
Disintegration involves breaking of at least some of the bonds between the polymer chains due to the exposure of the polymer to UV light (e.g., UV light coming from the sun), thus causing disintegration of the polymeric package into small pieces. Such small pieces, if not further decomposed, may remain in garbage yards or shelled portions for years. Composting or underground burial involves complete fragmentation of the polymer into carbon dioxide, water, inorganic compounds and biomass, leaving no distinguishable or toxic residues.
Composting processes are conducted at closed shelled portions, under controlled environment having controlled temperature and humidity levels, while underground burial requires the use of heavy machinery to cover the plastic residues. The composting process, or the underground degradation process, involves a digestion of the polymer by microorganisms into harmful compounds. Such polymers usually contain large amount of digestible material such as starch acting as the “substrate” for the microorganisms.
Full disintegration and fragmentation of a polymeric package or polymeric shells into carbon dioxide, water and other harmless compounds in open air, on the ground is very desirable. Furthermore, when being burned either accidentally or on-purpose it may be desirable that the product of the burning of the polymeric package will not contain any harmful gases.